I resealed this engine before putting it in my 81 Mustang racecar. Heads and deck flat, new head gaskets and ARP head studs torqued to 80 ftlbs.

When running at the track the cooling system pushes out quite a bit of coolant but according to logged data temp never passes 198*. After sitting over night there is still a bit of pressure on the cooling system, enough that it will not suck coolant back in. It is a 20psi cap, yes it is good, hose to overflow clear. I can run it at my house, burp air out and when it cools it will draw a bit in from the reservoir.... but running it at my house is not the same as running at the track, obviously.

I am thinking head gasket, but a bit odd to me that it is pushing out enough coolant to fill the overflow, about 2 qts, and still not running hoter than 198.

A racing buddie says this was a common iron head issue with the 5.0. Suggested starting with adding a bit more torque to the head studs.

Seems to get worse the harder I run it, as in running higher revs shifting later, that kind of thing. I have a block testing chemical, I will try it this weekend... but as I said I cant really run it hard at my house to get it super hot..

Combustion leak detector did not indicate a combustion leak, got it as hot as I could. No signs of burning coolant on any plugs. Re-torqued the head studs. Ill have to get it out to the track again to see how it does.

I will post up what happens, maybe it will help someone out in the future.